Dump truck hydraulic control



June 4, 1946. c, MONAH' N 2,401,498

DUMP TRUCK HYDRAULIC CONTROL Filed Oct. 18, 194:5 2 Sheets-Sheet 2 v INVENTORQ Patented June 4, 1946 DUMP raUoK HYDRAULIC CONTROL John C. Monahan, Detroit, Mich., assignor to Gar Wood Industries, Inc., Detroit, Mich., a

corporation of Michigan Application October 18,1943, Serial No. 506,643-

The present invention relates to a dump ve- 2 Claims. (Cl. 6054.5)

hicle construction and particularly relates to such constructions having an improved hydraulic dump mechanism associated therewith.

The primary object of the present invention is to provide an improved hydraulic dump mechanism by which; for a given or predetermined pump pressure, the dump cylinder pressure is automatically or selectively increased during the period of the hoisting stroke when the load is greatest and is then decreased to the pump pressure for the remainder of the hoisting stroke,

Other objects of the invention will become apparent from the following specification, the drawings relating thereto and from the claims hereinafter set forth.

In the drawings, in which like numerals are used to designate like. parts in the several views throughout:

Figure 1 is a side, perspective view of adump truck embodying features of the present invention and showing the body in its raised position; Fig. 2 is a top, perspective view of the hoist mechanism and showing such hoist mechanism in its association with the chassis and body; and, Fig. 3 is a diagrammatic view of the hydraulic control or power transmission system of the present invention.

In the operation of dump trucks, practically all hoists develop high pressures at the beginning of the stroke and lower pressures'at the end of the stroke. This is partly due to inertia, but mostly due to adverse leverage and load. According to the present invention, a pressure booster, in the form of a difierential piston fluid motor, is installed in the high pressure line with control means to automatically increase the work cylinder pressure without exceeding a predetermined or given pump pressure. The volume output from the booster need only be enough to raise the load initially 10 to 15. Thereafter, the body is moving-and as it moves the-leverages are much more favorable so that the lower pump pressure can handle the load without assistance,

Referring to the drawings, a dump truck is generally indicated at H! and includes the usual chassis I2, having a dump body It pivotally mounted adjacent the rear end ofthe chassis by means of a rear pivot l6. Hydraulic jacks, generally indicated at l8, are provided for hoisting or raising the'body and such jacks may be connected to the body and to the chassis by struc-z tures-such as those disclosed in the copending application of Louis S. Wood, Serial No. 418,115, filed November '1, 1941. Such hoisting means is shown by way of illustration, and it will be understood that other connections including the hydraulic jack may be employed within the scope of the present invention.

In the embodiment illustrated, two Jacks are employed but a single jack could be'used Within the scope of the present invention.

The jacks l8 include cylinders 20 having a piston 22 slidably disposed therein and having a piston rod 24 disposed to pass through the can end of the cylinder. The lower ends of the cylinders 20 are pivotally connected to the chassis by pivots indicated at'26. In the embodiment illustrated, the outer ends of the piston rods 24 are pivotally connected to a. lever member 28 by means of a pivot 30, located intermediate the ends of the lever 28, The forward endsof the lever 28 are pivotally connected to the body, as indicated at 32. Links 34 are pivotally connected to the opposite ends of the lever member by'pivots 36; and the opposite ends of the links The I 34 are'pivotall connected to pivots 26. structure so far described is substantially the same as that disclosed in the above-mentioned Wood application, except that here two cylinders are employed, rather than the one there disclosed.

It will be understood that as fluid is introduced into the inlet or lower ends of jacks l8,

that the piston rods 24 are extended to raise the body, as shown in Fig. l.

Referring to Fig. 3, the hydraulic power transmission system of the present invention and its association with the jacks is diagrammatically illustrated. As mentioned above, by the system of the present invention, higher unit pressures than the pump pressure are introduced into the hoist cylinder at the beginning of the stroke, for a limited period of the stroke, and thereafter the unit pressures introduced are those lower pressures directly from the pump. In the diagrammatic view illustrated only one of the jacks I8 is shown, but it will be understood that the ,two jacks maybe fed from the branch conduits leading from the inlet line.

The system includes a tank or reservoir 50,

.having an outlet conduit 52 communicating with .valve is of conventional construction.

An overload relief valve 60, having a conduit 62 associated with the conduit 56 and having municates with another port in valve 58 and returns to the tank 50. That much of the system so far described is conventional hydraulic pressure is effective through conduit 80 on the small area side of the piston but such piston will be moved to the right (viewing Fig. 3) in view of the larger effective area on the opposite side of the piston. As the differential piston 14 moves to the right, the higher unit pressures are developed on the small area side of the piston and such higher unit pressures are effective through conduit I02, close check valve I04, and pass through conduit 88 into the inlet of cylinder 20. The piston 22- will be moved to hoist the body at such high unit pressures until the piston 14 reaches the end hoist structure. It will be understood that with the valve 58in one osition, fluid under pressure is introduced to the lower end of cylinder 20, causing the body to be raised and fluid within the cylinder is then exhausted through conduit 88 and returns to the tank through valve 58 and conduit 10.. The predetermined or given pres-.

sure developed by the pump is the maximum pressure delivered to the work cylinder 20 and .the disadvantages mentioned above are present.

According to the present invention, a booster in the form of a differential piston, fluid motor comprising a cylinder I2 and a diilerential piston I4, is inserted in the system. The differential piston 14 is constructed and proportioned to give the desired difference in unit pressures and the length of the cylinder is such as to displace the desired volume for actuating the work cylinder over a desired period of time, or length of its stroke. A conduit I8 having branch conduits I8 of its stroke. At such time, the higher unit pressures will be no longer developed and the fluid will flow directly through check valve I04 at the given or predetermined pump pressures directly to the inlet to cylinder and the piston rod 24 will be extended to the' end of its stroke at the pump To return the body to its lower position, or to permit the piston 22 to return to its initial position, the valve 58 maybe shifted so that the pump pressure is introduced to cylinder 20 through conduit 68. The fluid on the underside of piston 22 then returns through conduit 68 and into conduit I02 (being checked against direct return by check valve I04) and into cylinder I2. This first position. The fluid within chamber 12, during the return of the differential piston 14 to its initial position, may exhaust through conduits I8 and 80 communicates with conduit 88. Conduit 80 communicates with the interior of cylinder 12 adjacent the inlet end of such cylinder but spaced slightly therefrom a distance slightly greater than the width of the piston, as illustrated. Conduit I8 communicates through the bottom or piston end of cylinder".

A control valve generally indicated at 82 is inserted in conduit I8. Such valve 82 has main passages 84 and 88 formed therein, such passages being communicable with each other through passageways 88 and 80. Communication between passages 84 and 88 through passageway 88 is controlled by means of a spring valve 92, which may be adjusted to open at a predetermined pressure. The space behind valve 82 may be exhausted to the tank through an exhaust conduit 84. A check valve 98 controls communication between passages .84 and 88 through passage 90 and is spring-urged in the direction shown. The space behind check valve 98 communicates with passage 84 by means of passage 88. Passages 84 and 88 are connected in conduit", as shown.

A conduit I02 communicates with cylinder I2 adjacent the cap end thereof and also communicates with conduit 88. A check valve I04 is inserted inconduit 88 between the points of communication oi conduits 18 and I02, and is constructed to check the flow of fluid back to the pump.

In the operation of the structure above de-. scribed, let it be assumed that the pump 84 is operated at its given or predetermined or normal unit pressure and that the valve 88 is set so that such fluid under pressure flows from conduit 88 into conduit 88. With the valve 82 designed or set to open at'a predetermined pressure, the fluid and and return to the tank through conduit 88, V

valve 58 and conduit 10. In the last portion of stroke, 011 flows through conduit 88, check valve From the structure and operation above de-' scribed, it will thus be seen that during the initial stage of hoisting, the unit pressures developed by the differential piston are increased over the pump pressures so that the work cylinder may b operated at these higher unit pressures during the initial stages of hoisting. The extent of the increase may be predetermined according to the relative areas ofthe opposite sides of differential piston 14.

Since the valve 82 is spring loaded, it will not be opened until the pressure exceeds a predetermined amount. Thus. in certain instances, for example, for a light. unloaded body, the flow from the pump would be directly through the check valve I04 to jack I8. Such flow would continue above. If the peak pressure does not occur at the been reached, and pass through passageway 88 into conduit I0 and into cylinder I2. The same beginning of the flrst stroke, the valve -82 may be set, or designed so that it does not open until the peak load is approached. The operation then is to direct the fluid first to the lacks I8, then through the booster 12,- and then directly to the iacksle.

It is also pointed out that the valve 82 may be omitted from conduit 18. When so omitted, the fluid from the pump will always pass first through the booster" at the initial stages of hoisting.

What is claimed is:

1. In an hydraulic control system, awork cylinder and piston assembly having a piston end and a rod end, a fluid pump, a flui conduit interconnecting the outlet of said pump with the piston end of said cylinder, a check valve in said conduit operative to prevent the return of fluid to said pump, a differential piston fluid motor having a low pressure inlet adjacent one end and a high pressure outlet adjacent the other end, said motor having a port intermediate the ends thereof, a fluid conduit interconnecting said high pressure outlet with said first named conduit between said work cylinder and said check valve, a fluid conduit interconnecting said port with said first named conduit between said pump and said check valve, a fluid conduit communicating with said last named fluid conduit and with said low pressure inlet,

6 with the piston end of said cylinder, a check valve in said conduit operative to prevent the return of fluid to said pump, a differential piston fluid motor having a low pressure inlet adjacent one end and a high pressure outlet adjacent the other end, said motor having a port intermediate the ends thereof, a fluid conduit interconnecting said high pressure outlet with said first named conduit betwen said work cylinder and said check valve, a fluid conduit interconnecting said port with said first named conduit between said pump and said check valve, a fluid conduit communicating with said last named fluid conduit and with said low a pressure inlet, a pressure opening valve in said being such that fluid returning from said work and a pressure opening valve in said last named v last named conduit, the construction and arrangement of said conduits, valves and motor cylinder through said first named fluid conduit returns through said second named conduit to said motor to first move the differential piston toward the low pressure end thereof, a reservoir, a fluid conduit connecting said reservoir with the inlet to said pump, a fluid conduit interconnecting the rod end of the work cylinder with the reservoir,' and-a control valve associated with said first and last two named conduits to control the flow of fluid through said conduits,

I JOHN C. MONAHAN. 

